Angewandte
Chemie
Wiley-VCH, Weinheim, 2000, chap. 10; b) S. E. Denmark, N. G.
3d–f (with three-, four-, and eight-carbon-atom tethers,
respectively) also underwent this tandem reaction (Table 1,
entries 8–14) in 20 minutes at 348C. This migration–elimina-
tion reaction can be rationalized by the following mechanism
on a three-carbon-atom tether (Scheme 3): (1-Butene)ZrCp2
reacts first with the remote double bond of 6 to form a
Almstead in Modern Carbonyl Chemistry (Ed.: J. Otera), Wiley-
VCH, Weinheim, 2000, chap. 11; c) Stereoselective Synthesis,
Methods of Organic Chemistry, Houben-Weyl, E21, Vol. 3 (Eds.:
G. Helmchen, R. Hoffmann, J. Mulzer, E. Schaumann), Thieme,
Stuttgart 1996; d) W. R. Roush in Comprehensive Organic
Synthesis, Vol. 2 (Eds. B. M. Trost, I. Fleming, C. H. Heathcock),
Pergamon, Oxford, 1991, p. 1; e) Y. Yamamoto, N. Asao, Chem.
Rev. 1993, 93, 2207.
À
zirconacyclopropane derivative 6a. Then, through allylic C
H bond activation,[12] the h3-allyl intermediate 6b is formed,
and after hydrogen migration the zirconacyclopropane 6c is
produced. By repeating the same sequence, the zirconacyclo-
propane 6e is finally obtained before its b elimination[15] into
the allylzirconocene intermediate 6 f. When a good leaving
group is used as in 3b (Table 1, entry 2), the major side
product thus obtained may be rationalized by the zirconium-
mediated conversion of homoallylic species into cyclopro-
pane derivatives, as shown by Szymoniak and co-workers,[16]
followed by dehydrozirconation into diene 9.[9] Therefore,
when the zirconium alcoholate is used as leaving group, the
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À
allylic C H bond activation of 6c into 6d is faster than the
1,3-elimination reaction (6c into 7).
[4] O. Desponds, L. Franzini, M. Schlosser, Synthesis 1997, 150, and
references therein.
In conclusion, (1-butene)ZrCp2 easily transforms
(20 minutes at 348C) unsaturated fatty alcohol derivatives
into allylzirconocene complexes through a tandem allylic
[5] a) P. Jones, N. Millot, P. Knochel, Chem. Commun. 1998, 2405;
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(Ed.: I. Marek), Wiley-VCH, Weinheim, 2002, p. 451.
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[8] a) J. J. Eisch in Comprehensive Organic Synthesis (Eds.: B. M.
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[9] a) U. Annby, S. Karlsson, S. Gronowitz, A. Hallberg, J. Alvhall,
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Hallberg, S. Gronowitz, Chem. Scr. 1988, 27, 185. If an excess of
the Schwartz reagent is used, the in situ formed terminal alkene
undergoes a further hydrozirconation reaction to give the
alkylzirconocene derivative.
À
C H activation–b-elimination reaction. The reaction seems
to be independent of the chain length between the unsatu-
rated system and the alcohol moiety. Extension of this new
preparative route to more elaborated structures is currently
under investigation.
Experimental Section
A solution of n-butyllithium in hexanes (4.8 equiv) was added
dropwise to a stirred solution of bis(cyclopentadienyl)zirconium
dichloride (2.4 equiv) in dry Et2O (15 mL) at À788C under argon
atmosphere. The temperature of the solution was allowed to reach
À58C and was then maintained for 5–6 min. The reaction mixture was
then cooled to À508C, and the alkenol 3c (1 equiv) in Et2O (5 mL)
was added dropwise to the solution, keeping the temperature at
À508C. When the addition was complete, the cooling bath was
removed and the reaction mixture was rapidly warmed to room
temperature. The solution was then heated and maintained at 348C
for 20 min to form the allylzirconocene intermediate (monitored by
GC of hydrolyzed aliquots), which is ready for further use[17] or,
alternatively, can be hydrolyzed with 1n HCl after cooling the
solution to room temperature. After hydrolysis, the layers were
separated and the aqueous phase was extracted four times with
diethyl ether. The combined organic extracts were washed succes-
sively with a saturated solution of sodium bicarbonate, brine, and then
dried over MgSO4. The obtained residue was finally purified by
column chromatography on silica gel to give the functionalized
alkenes as reported in Table 1.
[10] a) E. Negishi, T. Takahashi, Bull. Chem. Soc. Jpn. 1998, 71, 755;
b) E. Negishi, T. Takahashi, Acc. Chem. Res. 1994, 27, 124;
c) “Synthesis and Reactivity of Zirconocene Derivatives”: E.
Negishi, S. Huo in Titanium and Zirconium in Organic Synthesis
(Ed.: I. Marek), Wiley-VCH, Weinheim, 2002, p. 1.
Received: June 6, 2005
Revised: August 20, 2005
Published online: December 12, 2005
[11] N. Chinkov, S. Majumdar, I. Marek, J. Am. Chem. Soc. 2002, 124,
10282.
À
Keywords: alcohols · allylic compounds · C H activation ·
elimination · zirconium
.
[12] a) N. Chinkov, S. Majumdar, I. Marek, J. Am. Chem. Soc. 2003,
125, 13258; b) N. Chinkov, S. Majumdar, I. Marek, Synthesis
2004, 2411; c) “Stereoselective Synthesis of Dienyl Zirconocene
Complexes”: N. Chinkov, I. Marek in Topics on Organometallic
Chemistry, Vol. 10 (Ed.: I. Marek), Springer, Berlin, 2004, p. 133;
[1] For recent reviews of allylmetal addition, see a) S. R. Chemler,
W. R. Roush in Modern Carbonyl Chemistry (Ed.: J. Otera),
Angew. Chem. Int. Ed. 2006, 45, 465 –468
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